Heart rhythm problems or cardiac arrhythmias are a major cause of mortality and morbidity. An example of different rhythm problems encountered in clinical practice include atrial fibrillation (AF), cardiac arrest or sudden cardiac death (SCD) due to ventricular tachycardia/ventricular fibrillation (VT/VF), atrial flutter and other forms of atrial and ventricular arrhythnias. During the past 20 years, cardiac electrophysiology has evolved into a clinical tool to diagnose these cardiac arrhythmias. During electrophysiology studies multipolar catheters are positioned inside the heart and electrical recordings are made from the different chambers of the heart. Careful study of surface ECG and data from intracavitary electrograms is used conventionally to treat these arrhythmias.
Atrial fibrillation (AF), where the atria (upper chambers of the heart) stop contracting as they fibrillate or quiver, is the most common of the heart rhythm problems encountered in clinical practice. Recent data suggests AF is the most common arrhythmia-related cause of hospital admissions. Estimates indicate that 2.2 million people in the United States alone have AF and that 160,000 new cases are diagnosed every year. Patients with AF have a high incidence of such complications as stroke, and heart failure and bear an ominous prognosis of higher overall and cardiovascular mortality.
Recently it has been shown that premature atrial contractions can act as triggers and initiate paroxysms of AF. These premature ectopic beats have been shown to originate predominantly in the pulmonary veins. Inability to reproducibly identify the precise location of these trigger sites limits catheter ablation of trigger sites of AF.
Because of the critical role of the pulmonary veins in the generation of AF, and as infrequent and nonreproducible premature atrial contractions limit the utility of trigger site ablation, a variety of surgical and nonsurgical catheter ablation techniques have been used to isolate the pulmonary veins from the left atrium. An energy source such as radio-frequency waves are used to create a series of small scars on the heart's surface near the connection between the pulmonary veins and the left atrium. These scars stop the erratic impulses of atrial fibrillation by directing the impulses towards a normal electrical pathway through the heart.
Other strategic areas such as between the mitral annulus and the pulmonary veins, between the pulmonary veins, and between the left pulmonary veins and the left atrial appendage can also be targeted for ablation to increase the success rate in treating AF. Complete isolation of the pulmonary veins using various energy sources in patients undergoing open heart surgery has led to successful termination of AF in over 80% of patients. Although less invasive, trying to replicate this procedure non-surgically however is lengthy and labor intensive.
Sudden cardiac death is defined as an unexpected natural death from cardiac causes within a short period of time. Most SCDs are caused by VT/VF. It is estimated that SCD accounts for approximately 300,000 cardiac deaths in the United States alone each year. SCD is the most common and often the first manifestation of coronary artery disease and may be responsible for approximately 50% of deaths from cardiovascular disease in the United States. The most commonly encountered form of VT typically originates in the vicinity of a healed myocardial infarction. The mechanism of VT is reentry associated with myocardial scarring. However, these reentrant circuits are quite broad because of the nature of the scarring. The success rate of VT ablation would increase considerably if it were possible to precisely interrupt these broad reentrant circuits using lesions that transect them.
Several other arrhythmias such as atrial flutter, atrial tachycardias, and tachycardias involving accessory connections between the atria and ventricles are also extremely common and cause significant morbidity and some risk of higher mortality. Ablation between the tricuspid annulus and inferior vena cava, forming an anatomical barrier around the flutter circuit, can terminate atrial flutter. Similarly, the crista terminalis in the right atrium is a common source of atrial tachycardia. In this and other arrhythmias, the ability to precisely locate and identify these areas and to have a catheter apparatus that conforms to the particular 3D anatomy of each site so that ablation at that location is performed quickly and effectively would help significantly.
As specific locations such as the left atrium-pulmonary vein junction cannot be seen on fluoroscopy, multipolar catheters are usually positioned inside a heart chamber such as the left atrium after going through a blood vessel. These catheters are then swept around the cardiac chamber to gather electrophysiological information. The cardiac activation map acquired with such electrical readings is used to guide the catheters to specific locations showing double potentials. Such locations are suggestive of being sites capable of conducting impulses as between the pulmonary veins and the left atrium. Energy is then delivered by the catheters to ablate these locations.
Although helpful in certain instances, the inability to accurately relate the electrophysiologic information obtained to a specific anatomical location within the heart limits the usefulness of the readings to treat complex arrhythmias such as AF. The image created with the information is not an exact replication of the anatomy of these specific locations in the cardiac chamber. Moreover, the degree of resolution of this image is totally operator-dependent and limited by the time available to acquire the corresponding data points.
Current approaches of mapping and ablation, through their use of the currently available catheters to perform a point-by-point ablation within a complex 3D structure such as the left atrium guided by fluoroscopy and other techniques, makes the resulting ablation cumbersome, lengthy and inadequate. Since the true anatomy of the heart chamber is not being visualized, the unavailability of information on the size and orientation of such cardiac structures as the pulmonary veins and the pulmonary vein ostia contributes to the difficulty of such approaches. Given these limitations, the success rate of this procedure is low and only a limited number of patients may qualify for such treatment.
A number of modalities presently exist for improved medical diagnostic imaging. The most common ones for delineating anatomy include computed tomographic imaging (CT), magnetic resonance imaging (MRI) and x-ray systems. CT is both fast and accurate in collecting volumes of data over short acquisition times. This data has allowed for the 3D reconstruction of the underlying images into true and more understandable anatomic models. An approach that uses such 3D models for visualizing specific cardiac chambers and that provides endocardial (navigator or inside) views of such chambers to assist in the ablation of heart tissue at select locations would be highly desirable.
There is a need therefore for a catheter apparatus that can conform to the 3D anatomy of the pulmonary vein-left atrial junction and to other strategic areas in the heart so as to successfully more precisely and easily isolate the pulmonary veins and these other sites that initiate and sustain heart arrhythmias. There is also a need for a method that utilizes such catheter apparatus and allows for the visualization of the apparatus as it moves over a 3D model depicting the anatomy of a cardiac chamber such as the left atrium. Such a method would enable the rapid encircling of the pulmonary veins with a series of accurately placed lesions using radio-frequency or other forms of energy such as microwave, cryo-ablation and laser.